Arsenic concentrations and bacterial contamination in a pilot shallow dugwell program in West Bengal, India.

Project Well has developed a pilot self-supporting community-based mitigation program to provide arsenic-safe water to the villagers of North 24 Parganas, West Bengal, India. Shallow concrete dugwells, less than 25 feet deep, that tap into an unconfined aquifer are constructed following stipulated guidelines. The design differs from the traditional dugwell in two major ways: (i) there is a layer of coarse sand in the annular space enveloping the outer wall of the concrete cylinder; and (ii) handpumps are used for water extraction to reduce the potential for bacterial contamination. Monitoring programs for arsenic and coliform bacteria in selected dugwells have been completed. In summer, when the water levels were low, the arsenic concentrations were measured. In 11 wells, measured over three years, the average water arsenic concentration was 29 micro gL-1. Two dugwells had high concentrations of arsenic (average 152 micro gL-1 and 61 micro gL-1), but the remaining nine dugwells had an overall average of 11 micro gL-1. Seasonal variation was assessed in five wells with monthly measurements and there was a direct relationship between increases in arsenic concentrations and decreases in the volume of water in the dugwells in the dry summer season. To control bacterial contamination, sodium hypochlorite solution containing 5% chlorine was applied once a month. In 2005, fecal coliform was undetected in 65% (n = 13) of the dugwells but detected at high levels in 35% (n = 7) of the dugwells. The program clearly reduced exposure to arsenic, but we conclude that further study of increases in arsenic concentrations in the dry season are warranted, as well as assessment of ways to more effectively control bacterial contamination such as more frequent chlorination, perhaps with lower doses on each occasion.

Seasonal variation of arsenic concentrations in tubewells in west Bengal, India.

This study was conducted to monitor the changes in arsenic concentration during different seasons in a one-year period during 2002-2003 in selected tubewells in an arsenic-affected area in the district of South 24 Parganas in West Bengal, India, and to map the location of the wells. Seasonal variations in concentrations of arsenic in water were measured from 74 selected tubewells, ranging in depth from 40 to 500 feet. Water samples were collected from these wells during winter, summer, monsoon, and the following winter in 2002-2003. A global positioning system was used for locating the tubewells, and a geographic information system was used for mapping. There was evidence of seasonal variation in concentrations of arsenic in water (p=0.02) with the minimum average concentration occurring in the summer season (694 microg/L) and the maximum in the monsoon season (906 microg/L). From the winter of 2002 to the winter of 2003, arsenic concentrations increased, irrespective of the depth of the tubewells, from an average of 464 microg/L to 820 microg/L (p<0.001). This extent of variation in arsenic concentration, if confirmed, has important implications for both epidemiological research and mitigation programmes.

A dugwell program to provide arsenic-safe water in West Bengal, India: preliminary results.

In 1982, Dr. K. C. Saha, a dermatologist of Calcutta, West Bengal, identified patients with skin lesions from the district of 24 Parganas, leading him and others to search for a cause. The cause was soon identified to be arsenic in drinking water, but even today, 20 years later, large number of people continue to drink arsenic contaminated water and patients are increasing in number. Project Well is a program chosen for implementation in some villages of North 24 Parganas. Arsenic safe drinking water is provided for adopted villages by constructing shallow, concrete dugwells designed to tap the water of the unconfined aquifer, 20-30 feet below ground level, that contains low levels (< 0.05 mg/L) of arsenic in the target region. The traditional dugwell design is modified by use of tube well hand pumps to withdraw water. The project includes community involvement, programs to increase awareness of the need to drink arsenic safe water, and training in monitoring of dugwell water for arsenic and harmful pathogens. Disinfecting of the water and regulating the water hazard diagram are also included in the training program. The plan is to make the system sustainable at the village level using indigenous labor and materials.